The applicant's successful and popular vehicle recovery system sold under the trademark LoJack® includes a small electronic vehicle locating unit (VLU) with a transponder hidden within a vehicle, a private network of communication towers each with a remote transmitting unit (RTU), one or more law enforcement vehicles equipped with a vehicle tracking unit (VTU), and a network center with a database of customers who have purchased a VLU. The network center interfaces with the National Criminal Information Center. The entries of that database include the VIN number of the customer's vehicle and an identification code assigned to the customer's VLU.
When a LoJack® product customer reports that her vehicle has been stolen, the VIN number of the vehicle is reported to a law enforcement center for entry into a database of stolen vehicles. The network center includes software that interfaces with the database of the law enforcement center to compare the VIN number of the stolen vehicle with the database of the network center which includes VIN numbers corresponding to VLU identification codes. When there is a match between a VIN number of a stolen vehicle and a VLU identification code, as would be the case when the stolen vehicle is equipped with a VLU, and when the center has acknowledged the vehicle has been stolen, the network center communicates with the RTUs of the various communication towers (currently there are 180 nationwide) and each tower transmits a message to activate the transponder of the particular VLU bearing the identification code.
The transponder of the VLU in the stolen vehicle is thus activated and begins transmitting the unique VLU identification code. The VTU of any law enforcement vehicles proximate the stolen vehicle receive this VLU transponder code and, based on signal strength and directional information, the appropriate law enforcement vehicle can take active steps to recover the stolen vehicle. See, for example, U.S. Pat. Nos. 4,177,466, 4,818,988, 4,908,609, 5,704,008, 5,917,423, 6,229,988, 6,522,698, and 6,665,613 all incorporated herein by this reference.
Since the VLU unit is powered by the vehicle's battery, power management techniques must be employed in the VLU to ensure the VLU does not drain the vehicle's battery. One prior technique employed by the applicant includes programming the VLU to “wake up” and check for messages from the communication towers only periodically, e.g., every 8 seconds for 0.2 seconds. The timing of the sleep and wake-up modes was synchronized to the transmission schedule of one communication tower.
Historically, the vehicle locating unit was powered from the vehicle battery which made the vehicle locating unit vulnerable to any vagaries attendant on the vehicles own 20 power supply and power management controls. Today, certain vehicle manufacturers have power monitoring systems that do not allow use of their vehicle power: these systems may cut off power to any circuit that appears to be drawing too much current or is on too long, for example. Thus a vehicle locating unit connected to such circuits would be subject to being arbitrarily de-powered. One solution is to provide the vehicle locating unit with its own battery but this requires enlarging the size of the vehicle locating unit making it difficult to install in small, unobtrusive areas of the vehicle or using a smaller battery which results in shorter life e.g. six months with the attendant cost and effort of servicing the vehicle every six months for example.